This invention relates generally to automatic control systems for airplanes and in particular to an automatic control force trimming device for asymmetric engine failures.
When an engine fails on a multi-engine airplane, large asymmetric moments are generated. The asymmetric moments will cause uncontrolled flight and a crash unless corrective action is taken very quickly. Immediately after an engine failure corrective action requires rolling and yawing the airplane (with the wheel and rudder controls respectively) to counter the asymmetric moments. At the same time, airspeed must be maintained approximately equal to the best-rate-of-climb airspeed in order to keep from descending. However, during this time the control forces required of the pilot in the cockpit are extremely large. In order to relieve the majority of these forces and make the plane controllable, the airplane's secondary control surfaces or trim tabs must be retrimmed to the new asymmetric power condition.
In the past, on light, twin-engine propeller driven airplanes, the pilot has had to take all the corrective action himself, including retrimming the airplane. The dismal accident record of this class of airplanes after an engine failure leads to the conclusion that a device which lowers the pilot workload would be very beneficial. Conventional automatic control systems such as those in larger transports and other airplanes were never extensively used because they were too costly for light airplanes. In addition, they also required multiple sensors such as rate gyros, attitude gyros, linear accelerometers, and angle-of-sideslip vanes. Such systems would essentially be a "fly-by-wire" control system which would meet with intense pilot-owner and regulatory resistance because of the unique maintenance and reliability considerations of general aviation airplanes.
Thus, it is an object of the present invention to provide an automatic control system that would reduce the large control forces required of the pilot during an engine failure on a light, twin-engine propeller-driven airplane.
It is a further object of the present invention to provide a low cost automatic system to reduce the pilot workload in the event of an engine failure.
Another object of the present invention is to provide an automatic control system that is not fly-by-wire and allows for the pilot's direct control of the primary control surfaces.
A still further object of the present invention is to provide an automatic control system that reduces the large control force in the event of an engine failure that is simple and which has low maintenance requirements.
Other objects and advantages of the present invention will be readily apparent from the following description and drawings which illustrate a preferred embodiment of the present invention.